Earlier this month, in a post to his Facebook
page, WhatsApp CEO Jan Koum announced that his company’s instant messaging
service is now used by more than 900 million people. And then Facebook CEO Mark
Zuckerberg promptly responded with two posts of his own. One said “congrats,”
and the other included a cheeky photo Zuckerberg had taken of Koum as the
WhatsApp CEO keyed his 900-million-user post into a smartphone. “Here’s an
action shot of you writing this update,” Zuckerberg wrote.

WhatsApp is owned by Facebook, after
Zuckerberg and company paid $19 billion for the startup a little more than a
year ago. That means Facebook now runs three of the most popular apps on the
internet. Its primary social networking service is used by more than 1.5
billion people worldwide, and Facebook Messenger, an instant messaging service
spun off from Facebook proper, spans 700 million. But the 900 million-user
milestone announced by Koun is very much a WhatsApp achievement, not a product
of the formidable Facebook machine.

WhatsApp shows the way forward to a world where
internet services can serve a massive audience with help from few people.

One of the (many) intriguing parts of the
WhatsApp story is that it has achieved such enormous scale with such a tiny
team. When the company was acquired by Facebook, it had 35 engineers and
reached more than 450 million users. Today, it employs only about 50
engineers, though the number of WhatsApp users has doubled, and this tiny
engineering staff continues to run things almost entirely on its own. In a
world where so many internet services are rapidly expanding to millions upon
millions of users, WhatsApp shows the way forward—at least in part.

WhatsApp doesn’t talk much about its engineering
work—or any other part of its operation, for that matter—but yesterday, at an
event in San Jose, California, WhatsApp software engineer Jamshid Mahdavi took
the stage to briefly discuss the company’s rather unusual methods. Part of the
trick is that the company builds its service using a programming language
called Erlang. Though not all that popular across the wider coding community,
Erlang is particularly well suited to juggling communications from a huge
number of users, and it lets engineers deploy new code on the fly. But Mahdavi
says that the trick is as much about attitude as technology.

Mahdavi joined WhatsApp about two years ago,
after the startup was up and running, and its approach to engineering was
unlike any he had seen—in part because it used Erlang and a computer operating
system called FreeBSD, but also because it strove to keep its operation so
simple. “It was a completely different way of building a high-scale
infrastructure,” he said on Monday. “It was an eye-opener to see the
minimalistic approach to solving … just the problems that needed to be solved.”

Code in Parallel

In using Erlang, WhatsApp is part of a larger
push towards programming languages that are designed for concurrency, where
many processes run at the same time. As internet services reach more people—and
juggle more tasks from all those people—such languages become more attractive.
Naturally.

With its new anti-spam system—a system for
identifying malicious and otherwise unwanted messages on its social
network—Facebook uses a language called Haskell. Haskell began as a kind of
academic experiment in the late ’80s, and it’s still not used all that often.
But it’s ideal for Facebook’s spam fighting because it’s so good at juggling
parallel tasks—and because it lets coders tackle urgent tasks so quickly.
Meanwhile, Google and Mozilla, maker of the Firefox browser, are striving for a
similar sweet spot with new languages called Go and Rust.

In essence, WhatsApp is a replacement for
telecoms' texting services.

Like Haskell, Erlang is a product of the ’80s.
Engineers at Ericsson, the Swedish multinational that builds hardware and
software for telecom companies, developed the language for use with high-speed
phone networks. “Instead of inventing a language and then figuring out what to
do with it, they set out to invent a language which solved a very specific
problem,” says Francesco Cesarini, an Erlang guru based in the UK. “The problem
was that of massive scalability and reliability. Phone networks were the only
systems at the time who had to display those properties.”

Erlang remains on the fringes of the modern
coding world, but at WhatsApp and other internet companies, including WeChat
and Whisper, it has found a home with new applications that operate not unlike
a massive phone network. In essence, WhatsApp is a replacement for cellphone
texting services. It too requires that “scalability and reliability.”

What’s more, Erlang lets coders work at high
speed—another essential part of modern software development. It offers a way of
deploying new code to an application even as the application continues to run.
In an age of constant change, this is more useful than ever.

Keep It Simple, Smarty

The language does have its drawbacks. Relatively
few coders know Erlang, and it doesn’t necessarily dovetail with a lot of the
code already built by today’s internet companies. Facebook built its original
Facebook Chat app in Erlang but eventually rebuilt so that it would better fit
with the rest of its infrastructure. “You had this little island that was
Erlang, and it was hard to build enough boats back to the island to make
everything hook in,” says Facebook vice president of engineering Jay Parikh.

Of course, WhatsApp didn’t have to integrate with
an existing infrastructure in this way. And Mahdavi believes the relative
scarcity of Erlang coders isn’t a problem. “Our strategy around recruiting is
to find the best and brightest engineers. We don’t bring them in specifically
because the engineer knows Erlang,” Mahdavi said on Monday. “We expect the
engineer to come in and spend their first week getting familiar with the
language and learning to use the environment. If you hire smart people, they’ll
be able to do that.”

The company has succeeded by hiring engineers who
are adaptable—in more ways than one. Asked to explain the company’s secret,
Mahdavi’s response seems far too simple. But that’s the point. “The number-one
lesson is just be very focused on what you need to do,” he said. “Doing spend
time getting distracted by other activities, other technologies, even things in
the office, like meetings.”

At WhatsApp, employees almost never attend a
meeting. Yes, there are only a few dozen of them. But that too is the point.